1. Field of the Invention
This invention relates to a dynamic pressure fluid bearing, and particularly to a dynamic pressure fluid bearing for effectively ensuring a minute gap between the shaft of the dynamic pressure fluid bearing and a bearing.
2. Description of the Prior Art
In recent years, in high accuracy motors of which are required high speed, long life and low rotation irregularity, such as polygon mirror driving motors used in laser beam printers or the like, motors for VTR and motors for magnetic disk, dynamic pressure fluid bearings using gas such as air or liquid such as oil as the medium have been used because of their excellent bearing performance, low torque and low rotation irregularity during high-speed rotation. Such dynamic pressure fluid bearings are characterized by rotating in a non-contact state while keeping a minute gap (of the order of 2-10 .mu.) between the fixed side and the rotatable side during the steady state, and the bearing performance thereof (rotation accuracy, irregularity, torque, etc.) originates in such a characteristic.
Ensuring such gap is very important in preventing troubles fatal to the bearings such as the seizure of the fixed side and the rotatable side and deterioration of grease or oil due to abrasive powder.
For this reason, during the assembly, close attention is paid so that fine powder may not enter into the gap and the bearing surface may not be damaged, and consideration is also given to the motor itself as by hermetically sealing clean air so that no problem may occur once the motor has been accurately assembled.
However, there is no effective means for confirming the state immediately after the assembly and therefore, heretofore, there has been adopted a method of slightly floating the rotatable portion in the thrust direction (for example, in the motor of FIG. 1 of the accompanying drawings, a sleeve 5 is slightly floated and the throttle hole 7 of a thrust pad 6 is closed) and manually rotating the rotatable portion and confirming the contact sound by ear, or a method of gradually increasing the number of revolutions of the motor and observing the occurrence of abnormal sound and vibration, but both of these methods have been governed by the sixth sense of the operator and have been poor in working property and unsuitable for mass production.